The present invention relates to a base station using an adaptive array antenna and included in a radio communication system represented by a cellular radio communication system. The present invention is effective particularly in application to a system employing a code-division multiple access system (CDMA system) and controlling transmitting power for a downlink.
An adaptive array antenna (hereinafter abbreviated to “AAA”) has attracted a great deal of attention in recent years as mentioned in NTT DoCoMo Technical Journal, Vol. 5, No. 4, pp. 25–36 (June 1998). When applying an AAA to radio communication represented by cellular communication, the AAA is installed, in most cases, at a base station because the AAA has large construction.
There have been made many studies of the AAA relating to uplinks. Since the AAA forms an appropriate beam and does not radiate radio waves in undesired directions, it is expected that the capacity of downlinks can greatly be increased by using the AAA. In a time-division duplex system (hereinafter referred to as “TDD system”), an uplink and a downlink are used for the same frequency in a dime-division mode. Therefore, the timing of a pair of uplink and downlink is sufficiently small as compared with a fading frequency, the used propagation paths can be regarded as the same paths and transmission can be achieved by using the weight of the same array antenna as that for the uplink.
In a frequency-division duplex system (hereinafter referred to as “FDD system”), an uplink and a downlink use propagation paths of different frequencies. Therefore, array spaces for the uplink and the downlink differ from each other, so it is necessary that control is executed on the basis of a feedback signal from a terminal station or a propagation path for the downlink is predicted. Although the propagation paths change slightly between the uplink and the downlink, the bearing of a path connecting the base station and the terminal station changes scarcely because the bearing of the terminal station does not change. A method of estimating an array weight from bearing estimation by using such a property is proposed.